Epithelial sodium channels (ENaC) are multimeric, transmembrane channels located in the apical membranes of a wide variety of epithelial tissues, including the kidneys, lungs and the colon, where they play an important role in homeostasis by regulating salt/water reabsorption. The channels comprise three subunits: alpha or delta, beta and gamma. Modulators of ENaC have therapeutic potential in diseases that are related to ion conductance through ENaC channels, such as hypertension, pulmonary edema and cystic fibrosis.
The discovery of new and improved therapeutics that specifically target ENaC family members has been hampered by the lack of robust, physiologically relevant cell-based systems and more especially such systems that are amenable to high through-put formats for identifying and testing ENaC modulators. Cell-based systems are preferred for drug discovery and validation because they provide a functional assay for a compound as opposed to cell-free systems, which only provide a binding assay. Moreover, cell-based systems have the advantage of simultaneously testing cytotoxicity. Ideally, cell-based systems should also stably and constitutively express the target protein. It is also desirable for a cell-based system to be reproducible. With ENaC, this was not possible because ENaC is a heteromultimeric protein and ENaC expression was cytotoxic. The present invention addresses these problems.